1. Field of the Invention
The present invention relates to an extruded polymeric foam article and a process for preparing the extruded polymeric foam article.
2. Description of Related Art
Preparing extruded polymer foam that has desirable skin quality is challenging when using water as a blowing agent. Water tends to cause undesirable pinholes (also known as blowholes) that can disrupt a foam surface. Prior art references offer some ways to reduce undesirable effects of an aqueous blowing agent in preparing extruded foam.
PCT publication WO/2008/140892 discloses that use of a styrene-acrylonitrile (SAN) copolymer having a polydispersity index less than 2.5 in combination with a blowing agent comprising water and a fluorinated compound can produce polymer foam having a good skin quality that is free from blowholes. This reference does not characterize good skin quality in regards to smoothness, just in terms of visible defects. Even a foam surface that is free of visible defects can have a surface roughness detectible to the touch in the form of, for example, orange peel texturing.
U.S. Pat. No. 5,380,767 discloses that increasing the water solubility of a styrenic polymer composition or including an additive into the styrenic polymer composition that enhances the water solubility of the styrenic polymer composition can produce a closed-cell, monomodal foam from the styrenic polymer even with an aqueous blowing agent. This reference does not discuss quality of the resulting foam surface, particularly the smoothness of the foam surface.
International application number PCT/US09/038718 discloses use of SAN copolymer having a zero or positive skew in copolymerized acrylonitrile (AN) composition distribution that can produce extruded polymer foam having high quality surface skin, even with an aqueous blowing agent. This reference does not characterize good skin quality in regards to smoothness, just in terms of visible defects. Even a foam surface that is free of defects can have a surface roughness detectable to the touch.
It is desirable to further advance the art of preparing extruded thermoplastic polymer foam having a high quality surface skin, particularly a smooth skin, while using an aqueous blowing agent over these known methods.